Question: What excipient that's part carbon has the lowest refractive index?
Paraphrase: Which carbon excipient has the lowest refractive index?
SPARQL (Wikidata): select ?ent where { ?ent wdt:P31 wd:Q902638 . ?ent wdt:P1109 ?obj . ?ent wdt:P527 wd:Q623} ORDER BY ASC(?obj)LIMIT 5 
Answer: acetone, benzoic acid, acetophenone, calcium carbonate